1. Field of the Invention
The invention relates to recombinant promoters that are capable of driving tissue-specific expression, and transgenes comprising such recombinant promoters. In particular, the invention relates to transgenes comprising a recombinant promoter capable of driving tissue-specific expression of a heterologous nucleic acid molecule in a floral organ. The invention also relates to methods for using such transgenes to produce a protein in a host cell or transgenic plant. The invention further relates to methods for producing a transgenic plant that produces longer-lasting flowers as compared to a wild type plant.
2. Background of the Invention
Ethylene is a plant hormone that plays a critical role in regulating flower senescence in many species. Isolation of several components of the ethylene synthesis and signal transduction pathways has made possible the manipulation of ethylene responses through genetic modification. For example, overexpression of etr1-1, a mutant form of an Arabidopsis ethylene receptor caused decreased sensitivity to ethylene in petunia and carnation and delayed flower senescence. See e.g., Wilkinson et al., (1997) A dominant mutant receptor from Arabidopsis confers ethylene insensitivity in heterologous plants. Nat. Biotechnol. 15: 444–447; Bovy et al., (1999) Heterologous expression of the Arabidopsis etr1-1 allele inhibits the senescence of carnation flowers. Mol. Breed. 5: 301–308).
Although manipulation of ethylene responses is useful to prevent flower senescence, there are several potential disadvantages to this approach. The greatest disadvantage is that where constitutive promoters, such as Cauliflower mosaic virus 35S promoters, were used to drive transgene expression, changes occurred in ethylene response even in untargeted tissues. In fact, etr1-1 has been shown to have negative effects when expressed ectopically in vegetative tissues such as roots and stems. For example, ethylene-insensitive petunia that harbors Cauliflower mosaic virus 35S promoter driven etr1-1 displays reduced adventitious rooting. See e.g., Clark et al., (1999) Root formation in ethylene-insensitive plants. Plant Physiol. 121: 53–60. These plants also show a great deal of premature death. See e.g., Shibuya et al., (2004) The central role of PhEIN2 in ethylene responses throughout plant development in petunia (Unpublished). Furthermore, overexpression of etr1-1 in tobacco increased susceptibility to fungal pathogens infecting roots. See e.g., Knoester et al., (1998) Ethylene-insensitive tobacco lacks non-host resistance against soil-borne fingi. Proc. Natl. Acad. Sci. 95: 1933–1937. Thus, altering ethylene sensitivity throughout the plant causes negative effects in untargeted tissues.
Therefore, there remains a need in the art for recombinant promoters that are capable of driving tissue-specific expression of an isolated nucleic acid molecule operably linked to the promoter. In particular, there is a need in the art for recombinant promoters that are capable of driving expression of isolated nucleic acid molecules in a floral organ, and transgenes comprising such recombinant promoters. The development of such transgenes would have wide application in the production of transgenic plants expressing commercially desirable proteins, such as ethylene receptor etr1-1, in floral organs.